The invention of the present application relates to a valve timing control system for an internal combustion engine, which controls the opening/closing timing of an intake valve and/or an exhaust valve in accordance with the engine operating conditions.
A typical valve timing control system is disclosed in Japanese document JP-A 11-159311. This valve timing control system comprises a housing linked to a crankshaft through a chain, etc. and a vane rotor integrally coupled to a camshaft. The housing and the vane rotor are assembled to be rotatable relative to each other, and the assembling angle therebetween, i.e. the relative rotated position, is changed in accordance with the engine operating conditions. The housing comprises a plurality of partition walls to protrude radially inward, whereas the vane rotor comprises a cylindrical main body arranged in the center of the housing and with which the front ends of the partition walls make slide contact, and vanes arranged to protrude radially from the vane-rotor main body to define advance and retard chambers between adjacent partition walls. The advance and retard chambers are connected to hydraulic-pressure supply/discharge means for selectively switching between supply and discharge of working fluid in accordance with the engine operating conditions.
The housing comprises a main body having a peripheral wall and a partition wall and a sidewall member for closing a side portion of the housing main body on the camshaft side. The sidewall member is formed with a bearing hole for supporting a shank of the camshaft on the front-end side. Supply/discharge of working fluid to one of the advance and retard chambers is carried out via a supply/discharge passage extending from the camshaft through the bearing hole to the sidewall member.
Specifically, the camshaft has a communication passage formed therethrough to extend radially outward from a shaft passage formed along the center of the camshaft, and an annular groove formed in the outer peripheral surface and to which the communication passage opens. The sidewall member is formed with a connection passage for connecting the annular groove of the camshaft to one of the advance and retard chambers. The communication passage of the camshaft and the connection passage of the sidewall member are always in fluid communication via the annular groove.